1. Field of the Invention
The present invention is directed to a temperature-protected semiconductor switch having a semiconductor switch element which is composed of a number of cells connected in parallel and which includes an integrated reverse diode. The temperature-protected semiconductor switch also has a temperature sensor wherein the semiconductor switch element and the temperature sensor are integrated together in a semiconductor body of a first conductivity type and wherein the temperature sensor generates a first signal given the occurrence of an excessive temperature.
2. Description of the Prior Art
For protection against thermal overload, semiconductor switches, particularly power switches, are provided with integrated temperature sensors. The temperature sensors acquire the temperature of the power switch and convert this into a temperature-dependent, analog signal which then can be interpreted in a circuit. As a result thereof, for example, a shut-off of the semiconductor switch is possible when a specific, predetermined temperature has been exceeded.
FIG. 1a shows a schematic view of such a semiconductor switch. The semiconductor switch 1 is thereby composed of a semiconductor switch element T1, for example a MOSFET, that includes a number of cells (not shown) connected in parallel. A temperature sensor TS is integrated in the proximity of the hottest location; this being potentially implemented, for example, as a diode, a bipolar transistor or, on the other hand, as a thyristor. The temperature sensor TS together with the semiconductor switch element T1 is integrated in a semiconductor body. Via a signal line SL1, the temperature sensor TS outputs a signal when a predetermined temperature is upwardly exceeded, this signal being processed by an evaluation unit (not shown). The signal then can be taken to shut the semiconductor switch element T1 off. As a result, an overheating and, thus, a destruction of the semiconductor switch element T1 can be avoided. FIG. 1b shows the schematic circuit diagram of the semiconductor switch element T1, a MOSFET, and of the temperature sensor TS. Due to technology, a MOSFET includes an integrated reverse diode D1. Many versions are known for the interconnection of a temperature sensor TS with the semiconductor switch element so that only a block symbol is shown for the temperature sensor; this being connected to a status output ST1 via the signal line 1. A circuit arrangement for acquiring the excess temperature of a semiconductor switch in integrated form is disclosed, for example, by EP 0 341 482 A1.
When the temperature sensor together with the semiconductor switch element is integrated in a semiconductor body, the technologically integrated diode can present problems for the semiconductor switch element from source to drain. When this is operated statically or temporarily in flow direction, it produces free charge carriers. The free charge carriers form a parasitic structure together with the integrated temperature sensor. This can lead to the fact that the temperature sensor assumes it has detected an excess temperature and, thus, outputs a signal to the evaluation. This case can occur, for example, when respectively two temperature-protected high-side and low-side switches are interconnected to form a H-bridge and when a motor represents the load. Since the motor represents an inductance, reactance currents can activate the integrated reverse diode and produce free charge carriers.
In order to prevent this undesired condition, it is known to integrate the temperature sensor with a suitable, permanently implanted charge carrier diffusion that annularly surrounds the temperature sensor. The emitted charge carriers can be captured by applying a voltage between the charge carrier diffusion and the integrated reverse diode. As a result thereof, the temperature sensor is protected against the penetration of charge carriers. The charge carrier diffusion rings, which are also referred to as “suction rings”, however, have only a limited effect given high currents through the integrated reverse diode. In order also to be able to capture the charge carriers given high currents, the charge carrier diffusion would have to be implemented extremely broad. This, however, would have the disadvantageous effect that the temperature sensor exhibits a relatively great distance from the hottest location of the semiconductor switch element. It is precisely in semiconductor switches with a high current density, however, that the reaction time of the temperature sensor given thermal overload of the semiconductor switch element is of great significance. When, on the other hand, the charge carrier diffusion is implemented too low, this cannot adequately efficiently protect the temperature sensor given extremely high currents through the reverse diode D1 in order to prevent the undesired, parasitic effects to the temperature sensor.
Proceeding on the basis of this prior art, therefore, an object of the present invention is to provide a temperature-protected semiconductor switch that enables the response of the temperature sensor in a simple way only in case of an excess temperature.